/*
 *  Licensed to the Apache Software Foundation (ASF) under one or more
 *  contributor license agreements.  See the NOTICE file distributed with
 *  this work for additional information regarding copyright ownership.
 *  The ASF licenses this file to You under the Apache License, Version 2.0
 *  (the "License"); you may not use this file except in compliance with
 *  the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *  Unless required by applicable law or agreed to in writing, software
 *  distributed under the License is distributed on an "AS IS" BASIS,
 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *  See the License for the specific language governing permissions and
 *  limitations under the License.
 *
 */

/*
 * This package is based on the work done by Timothy Gerard Endres
 * (time@ice.com) to whom the Ant project is very grateful for his great code.
 */

package org.apache.tools.tar;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.Arrays;

/**
 * The TarBuffer class implements the tar archive concept of a buffered input stream. This concept goes back to the days of blocked tape drives and special io
 * devices. In the Java universe, the only real function that this class performs is to ensure that files have the correct "block" size, or other tars will
 * complain.
 * <p>
 * You should never have a need to access this class directly. TarBuffers are created by Tar IO Streams.
 * 
 */

public class TarBuffer {

  /** Default record size */
  public static final int      DEFAULT_RCDSIZE = (512);

  /** Default block size */
  public static final int      DEFAULT_BLKSIZE = (TarBuffer.DEFAULT_RCDSIZE * 20);

  private InputStream          inStream;
  private OutputStream         outStream;
  private byte[]               blockBuffer;
  private int                  currBlkIdx;
  private int                  currRecIdx;
  private int                  blockSize;
  private int                  recordSize;
  private int                  recsPerBlock;
  private final static boolean debug           = false;

  /**
   * Constructor for a TarBuffer on an input stream.
   * 
   * @param inStream
   *          the input stream to use
   */
  public TarBuffer(final InputStream inStream) {
    this(inStream, TarBuffer.DEFAULT_BLKSIZE);
  }

  /**
   * Constructor for a TarBuffer on an input stream.
   * 
   * @param inStream
   *          the input stream to use
   * @param blockSize
   *          the block size to use
   */
  public TarBuffer(final InputStream inStream, final int blockSize) {
    this(inStream, blockSize, TarBuffer.DEFAULT_RCDSIZE);
  }

  /**
   * Constructor for a TarBuffer on an input stream.
   * 
   * @param inStream
   *          the input stream to use
   * @param blockSize
   *          the block size to use
   * @param recordSize
   *          the record size to use
   */
  public TarBuffer(final InputStream inStream, final int blockSize, final int recordSize) {
    this.inStream = inStream;
    this.outStream = null;

    this.initialize(blockSize, recordSize);
  }

  /**
   * Constructor for a TarBuffer on an output stream.
   * 
   * @param outStream
   *          the output stream to use
   */
  public TarBuffer(final OutputStream outStream) {
    this(outStream, TarBuffer.DEFAULT_BLKSIZE);
  }

  /**
   * Constructor for a TarBuffer on an output stream.
   * 
   * @param outStream
   *          the output stream to use
   * @param blockSize
   *          the block size to use
   */
  public TarBuffer(final OutputStream outStream, final int blockSize) {
    this(outStream, blockSize, TarBuffer.DEFAULT_RCDSIZE);
  }

  /**
   * Constructor for a TarBuffer on an output stream.
   * 
   * @param outStream
   *          the output stream to use
   * @param blockSize
   *          the block size to use
   * @param recordSize
   *          the record size to use
   */
  public TarBuffer(final OutputStream outStream, final int blockSize, final int recordSize) {
    this.inStream = null;
    this.outStream = outStream;

    this.initialize(blockSize, recordSize);
  }

  /**
   * Initialization common to all constructors.
   */
  private void initialize(final int blSize, final int recSize) {
    this.blockSize = blSize;
    this.recordSize = recSize;
    this.recsPerBlock = (this.blockSize / this.recordSize);
    this.blockBuffer = new byte[this.blockSize];

    if (this.inStream != null) {
      this.currBlkIdx = -1;
      this.currRecIdx = this.recsPerBlock;
    } else {
      this.currBlkIdx = 0;
      this.currRecIdx = 0;
    }
  }

  /**
   * Get the TAR Buffer's block size. Blocks consist of multiple records.
   * 
   * @return the block size
   */
  public int getBlockSize() {
    return this.blockSize;
  }

  /**
   * Get the TAR Buffer's record size.
   * 
   * @return the record size
   */
  public int getRecordSize() {
    return this.recordSize;
  }

  /**
   * Determine if an archive record indicate End of Archive. End of archive is indicated by a record that consists entirely of null bytes.
   * 
   * @param record
   *          The record data to check.
   * @return true if the record data is an End of Archive
   */
  public boolean isEOFRecord(final byte[] record) {
    for (int i = 0, sz = this.getRecordSize(); i < sz; ++i) {
      if (record[i] != 0) {
        return false;
      }
    }

    return true;
  }

  /**
   * Skip over a record on the input stream.
   * 
   * @throws IOException
   *           on error
   */
  public void skipRecord() throws IOException {
    if (TarBuffer.debug) {
      System.err.println("SkipRecord: recIdx = " + this.currRecIdx + " blkIdx = " + this.currBlkIdx);
    }

    if (this.inStream == null) {
      throw new IOException("reading (via skip) from an output buffer");
    }

    if (this.currRecIdx >= this.recsPerBlock) {
      if (!this.readBlock()) {
        return; // UNDONE
      }
    }

    this.currRecIdx++;
  }

  /**
   * Read a record from the input stream and return the data.
   * 
   * @return The record data.
   * @throws IOException
   *           on error
   */
  public byte[] readRecord() throws IOException {
    if (TarBuffer.debug) {
      System.err.println("ReadRecord: recIdx = " + this.currRecIdx + " blkIdx = " + this.currBlkIdx);
    }

    if (this.inStream == null) {
      return null;
    }

    if (this.currRecIdx >= this.recsPerBlock) {
      if (!this.readBlock()) {
        return null;
      }
    }

    final byte[] result = new byte[this.recordSize];

    System.arraycopy(this.blockBuffer, (this.currRecIdx * this.recordSize), result, 0, this.recordSize);

    this.currRecIdx++;

    return result;
  }

  /**
   * @return false if End-Of-File, else true
   */
  private boolean readBlock() throws IOException {
    if (TarBuffer.debug) {
      System.err.println("ReadBlock: blkIdx = " + this.currBlkIdx);
    }

    if (this.inStream == null) {
      throw new IOException("reading from an output buffer");
    }

    this.currRecIdx = 0;

    int offset = 0;
    int bytesNeeded = this.blockSize;

    while (bytesNeeded > 0) {
      final long numBytes = this.inStream.read(this.blockBuffer, offset, bytesNeeded);

      //
      // NOTE
      // We have fit EOF, and the block is not full!
      //
      // This is a broken archive. It does not follow the standard
      // blocking algorithm. However, because we are generous, and
      // it requires little effort, we will simply ignore the error
      // and continue as if the entire block were read. This does
      // not appear to break anything upstream. We used to return
      // false in this case.
      //
      // Thanks to 'Yohann.Roussel@alcatel.fr' for this fix.
      //
      if (numBytes == -1) {
        if (offset == 0) {
          // Ensure that we do not read gigabytes of zeros
          // for a corrupt tar file.
          // See http://issues.apache.org/bugzilla/show_bug.cgi?id=39924
          return false;
        }
        // However, just leaving the unread portion of the buffer dirty does
        // cause problems in some cases. This problem is described in
        // http://issues.apache.org/bugzilla/show_bug.cgi?id=29877
        //
        // The solution is to fill the unused portion of the buffer with zeros.

        Arrays.fill(this.blockBuffer, offset, offset + bytesNeeded, (byte) 0);

        break;
      }

      offset += numBytes;
      bytesNeeded -= numBytes;

      if (numBytes != this.blockSize) {
        if (TarBuffer.debug) {
          System.err.println("ReadBlock: INCOMPLETE READ " + numBytes + " of " + this.blockSize + " bytes read.");
        }
      }
    }

    this.currBlkIdx++;

    return true;
  }

  /**
   * Get the current block number, zero based.
   * 
   * @return The current zero based block number.
   */
  public int getCurrentBlockNum() {
    return this.currBlkIdx;
  }

  /**
   * Get the current record number, within the current block, zero based. Thus, current offset = (currentBlockNum * recsPerBlk) + currentRecNum.
   * 
   * @return The current zero based record number.
   */
  public int getCurrentRecordNum() {
    return this.currRecIdx - 1;
  }

  /**
   * Write an archive record to the archive.
   * 
   * @param record
   *          The record data to write to the archive.
   * @throws IOException
   *           on error
   */
  public void writeRecord(final byte[] record) throws IOException {
    if (TarBuffer.debug) {
      System.err.println("WriteRecord: recIdx = " + this.currRecIdx + " blkIdx = " + this.currBlkIdx);
    }

    if (this.outStream == null) {
      throw new IOException("writing to an input buffer");
    }

    if (record.length != this.recordSize) {
      throw new IOException("record to write has length '" + record.length + "' which is not the record size of '" + this.recordSize + "'");
    }

    if (this.currRecIdx >= this.recsPerBlock) {
      this.writeBlock();
    }

    System.arraycopy(record, 0, this.blockBuffer, (this.currRecIdx * this.recordSize), this.recordSize);

    this.currRecIdx++;
  }

  /**
   * Write an archive record to the archive, where the record may be inside of a larger array buffer. The buffer must be "offset plus record size" long.
   * 
   * @param buf
   *          The buffer containing the record data to write.
   * @param offset
   *          The offset of the record data within buf.
   * @throws IOException
   *           on error
   */
  public void writeRecord(final byte[] buf, final int offset) throws IOException {
    if (TarBuffer.debug) {
      System.err.println("WriteRecord: recIdx = " + this.currRecIdx + " blkIdx = " + this.currBlkIdx);
    }

    if (this.outStream == null) {
      throw new IOException("writing to an input buffer");
    }

    if ((offset + this.recordSize) > buf.length) {
      throw new IOException("record has length '" + buf.length + "' with offset '" + offset + "' which is less than the record size of '" + this.recordSize
          + "'");
    }

    if (this.currRecIdx >= this.recsPerBlock) {
      this.writeBlock();
    }

    System.arraycopy(buf, offset, this.blockBuffer, (this.currRecIdx * this.recordSize), this.recordSize);

    this.currRecIdx++;
  }

  /**
   * Write a TarBuffer block to the archive.
   */
  private void writeBlock() throws IOException {
    if (TarBuffer.debug) {
      System.err.println("WriteBlock: blkIdx = " + this.currBlkIdx);
    }

    if (this.outStream == null) {
      throw new IOException("writing to an input buffer");
    }

    this.outStream.write(this.blockBuffer, 0, this.blockSize);
    this.outStream.flush();

    this.currRecIdx = 0;
    this.currBlkIdx++;
    Arrays.fill(this.blockBuffer, (byte) 0);
  }

  /**
   * Flush the current data block if it has any data in it.
   */
  void flushBlock() throws IOException {
    if (TarBuffer.debug) {
      System.err.println("TarBuffer.flushBlock() called.");
    }

    if (this.outStream == null) {
      throw new IOException("writing to an input buffer");
    }

    if (this.currRecIdx > 0) {
      this.writeBlock();
    }
  }

  /**
   * Close the TarBuffer. If this is an output buffer, also flush the current block before closing.
   * 
   * @throws IOException
   *           on error
   */
  public void close() throws IOException {
    if (TarBuffer.debug) {
      System.err.println("TarBuffer.closeBuffer().");
    }

    if (this.outStream != null) {
      this.flushBlock();

      if ((this.outStream != System.out) && (this.outStream != System.err)) {
        this.outStream.close();

        this.outStream = null;
      }
    } else if (this.inStream != null) {
      if (this.inStream != System.in) {
        this.inStream.close();

        this.inStream = null;
      }
    }
  }
}
